Nowadays a number of endemic mosquito species are known to possess vector abilities for various diseases, as e.g. the sibling species Culex pipiens and Culex torrentium. Due to their morphological similarity, ecology, distribution and vector abilities, knowledge about these species' population structure is essential. Culicidae from 25 different sampling sites were collected from March till October 2012. All analyses were performed with aligned cox1 sequences with a total length of 658 bp. Population structure as well as distribution patterns of both species were analysed using molecular methods and different statistical tests like distance based redundancy analysis (dbDRA), analysis of molecular variances (AMOVA) or McDonald & Kreitman test and Tajima's D. Within both species, we could show a genetic variability among the cox1 fragment. The construction of haplotype networks revealed one dominating haplotype for Cx. pipiens, widely distributed within Germany and a more homogeneous pattern for Cx. torrentium. The low genetic differences within Cx. pipiens could be a result of an infection with Wolbachia which can induce a sweep through populations by passively taking the also maternally inherited mtDNA through the population, thereby reducing the mitochondrial diversity as an outcome of reproductive incompatibility. Pairwise population genetic differentiation (FST) ranged significantly from moderate to very great between populations of Cx. pipiens and Cx. torrentium. Analyses of molecular variances revealed for both species that the main genetic variability exists within the populations (Cx. pipiens [88.38%]; Cx. torrentium [66.54%]). Based on a distance based redundancy analysis geographical origin explained a small but significant part of the species' genetic variation. Overall, the results confirm that Cx. pipiens and Cx. torrentium underlie different factors regarding their mitochondrial differentiation, which could be a result of endosymbiosis, dispersal between nearly located populations or human introduction.

During the last couple of decades, invasive species have become a worldwide problem in many freshwater systems. Besides higher plants and animals, microbes, in particular the potentially toxic cyanobacterium Cylindrospermopsis raciborskii, has attracted increasing attention, due to its spread towards temperate zones of the northern and southern hemisphere. A number of advantageous functional traits and a high intraspecific plasticity have been suggested to explain its invasion success. The aim of this study was to examine intraspecific functional trait variability in 12 different isolates of C. raciborskii originating from different lakes in an invaded region in Northeast Germany. We measured growth rate, C:N:P ratios, chlorophyll‐a content and the abundance of heterocysts under nutrient‐replete and phosphorus‐limited conditions. Moreover, the isolate‐specific morphology and grazing losses by an herbivorous rotifer, as a top‐down force, were studied. DNA fingerprinting revealed that all isolates were genetically different. C. raciborskii exhibited a large variability in all measured traits among isolates. The C:P, N:P and Chl‐a:C ratios differed by a factor of two or more. The trait variability among isolates was higher under nutrient‐replete conditions, except for the C:P ratio, which varied most during phosphorus limitation. The susceptibility to grazing, calculated as maximum ingestion rates of the rotifer Brachionus calyciflorus on C. raciborskii, varied most among isolates, but was not related to any of the measured physiological or morphological traits, i.e. no trade‐off was found. Ecological and genetic clustering did not match, indicating that the genetic relationship based on DNA fingerprinting did not cover ecological differences. Our results show a high trait variability within locally occurring and partly co‐occurring C. raciborskii isolates. No overall trade‐offs between the measured functional traits were found. This demonstrates the ecological relevance of linking multiple traits, e.g. competitive and consumptive. Furthermore, this study emphasises the importance of analysing more than one strain of a species, as different strains show different trait values potentially relevant for their invasibility and the field of general trait‐based ecology.

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Culex torrentium is one of the most common mosquito species in Germany. Due to its sympatric occurrence as well as its similar morphological and ecological characteristics, it has often been confused with another common species, Culex pipiens. Both species are known to be potential vectors for different arboviruses (not only in Germany) with C. torrentium being a possible vector for Sindbis or Ockelbo virus. In our study, we analyzed the genetic variability in a 658 bp fragment of the cytochrome c oxidase subunit I gene (coxI) of C. torrentium, from nine localities in the Frankfurt/Rhine-Main Metropolitan Region. The results of our genetic survey indicate a higher genetic diversity in this gene region for C. torrentium than for the morphologically similar C. pipiens. Our findings may explain the difficulties in the past to find morphological characteristics that apply to all populations of C. torrentium, when attempting to separate them clearly from C. pipiens, by any other criteria than male genitalia. Being ornithophilic, possible hybrids between C. torrentium and the humanophilic C. pipiens biotype molestus, could potentially serve as important vectors for zoonotic diseases. Therefore, we recommend that greater emphasis is placed on the ecological characteristics, population structure, and the taxonomy of this often neglected species, in the future.

Biological invasions are a major threat to biodiversity and ecosystem functioning. Successful invasions depend on the interplay of multiple abiotic and biotic factors, however, the process of the invasion itself is often overlooked. The temporal variation of environmental factors suggests that a ‘window of opportunity’ for successful invasions exists. Especially aquatic habitats, like temperate lakes, undergo pronounced seasonal fluctuations and show temporally varying environmental conditions in e.g. nutrient availability, temperature and the composition of the resident community including competitors and consumers. We experimentally tested if an invasion window for the globally invasive cyanobacterium Cylindrospermopsis raciborskii exists. From May to September, we determined the invasion success of C . raciborskii in laboratory mesocosms with natural lake water. Although the invasion success was generally low, the invasiveness varied among months and differed in total invasive biomass, net development and final share of C . raciborskii in the community. During the first days, C . raciborskii strongly declined and this initial, short-term decline was independent of the ambient consumptive pressure. These results are in contrast to laboratory studies in which C . raciborskii successfully invaded, suggesting that a complex natural system develops a resistance to invasions.